Anti-melanoma differentiation-associated gene 5 (MDA5) antibody-positive dermatomyositis responds to rituximab therapy

Objectives The purpose of this study was to assess the efficacy of rituximab (RTX) in the management of anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibody-positive dermatomyositis (DM), with or without rapidly progressive interstitial lung disease (RP-ILD). Methods Medical records of DM patients with anti-MDA5 antibodies treated with RTX therapy were reviewed retrospectively. Skin rash data, lung function tests, chest high-resolution computed tomography (HRCT), and serum markers were compared before and after RTX. Results Eleven consecutive cases, including 5 males and 6 females, were identified. One hundred percent of patients had a typical DM rash and about 45% presented with skin ulceration. All the patients had ILD, 73% had RP-ILD, and 27% had mild or asymptomatic ILD. Ro-52 antibodies were found in 55% of this group. Lymphopenia was present in 10/11 patients (91%). Around half (55%) had a level of ferritin greater than 1000 ng/ml. Nine patients (82%) were refractory. These patients received intravenous RTX (375 mg/m 2 ) at 0 and 14 days (conventional dose) or 100 mg once a week for 4 weeks (low dose). After RTX treatment, 2 patients (18%) with mild ILD showed complete remission, and 6 (55%) showed improvement in lung HRCT and/or lung function. Skin rash in 4 patients (100%) and ILD in 3 (75%) showed improvement in the low-dose group. Infection episodes occurred in four (57%) and one (25%) of the conventional-dose and low-dose group, respectively. Conclusions Our study found that RTX is sufficient to improve skin rash and ILD or RP-ILD. Our results also suggest that lower RTX doses may be a useful therapy for anti-MDA5 antibody-positive DM patients. Key Points • To clarify efficacy of RTX in the management of anti-MDA5 antibody-positive DM, we performed a retrospective chart review of DM patients with anti-MDA5 antibodies who were treated with RTX. • This study found that RTX is sufficient to improve skin rash and ILD or RP-ILD. • The results suggest that low-dose RTX in treatment of MDA5-DM results in better responses and fewer adverse events.